Viscosity perturbation damper connected with distribution header of papermaking machine headbox

ABSTRACT

One or more viscosity perturbation dampers are connected in the branch pipe of the short circulation link leading to a papermaking machine headbox. The dampers operate according to the multiple delay principle and consist of parallel pipes which are connected by a plurality of parallel intermediate pipes such that the stock flow reverses direction after having been split up in passing through the parallel intermediate pipes. These intermediate parallel pipes may include vortex purifiers or pressure strainers.

llnite ll: ayala States [4 1 Feb. 11, 1975 VHSCOSHTY PERTURBATHON DAMPER CONNECTED WlTl-ll DISTRHBUTKON HEADER 0F PAPERMAKRNG MACHTNE HEADBOX lnventor: Matti Rajala, Tampere, Finland Assignee: Valmet 0y, Helsinki, Finland Filed: Aug. 9, 1973 Appl. No: 387,133

Foreign Application Priority lData Aug. 15, 1972 Finland 2260/72 U.S. Cl 162/343, 162/216, 162/264 lnt. Cl. 1021f 1/06 Field of Search 162/212, 216, 343, 380, 162/216, 343, 264

References Cited UNITED STATES PATENTS Means 162/216 3,725,197 4/1973 Dahl et al. 162/343 Primary ExaminerS. Leon Bashore Assistant Examiner-Richard H. Tushin Attorney, Agent, or Firm-Richards & Geier [57] ABSTRACT One or more viscosity perturbation dampers are connected in the branch pipe of the short circulation link leading to a papermaking machine headbox. The dampers operate according to the multiple delay principle and consist of parallel pipes which are connected by a plurality of parallel intermediate pipes such that the stock flow reverses direction after having been split up in passing through the parallel intermediate pipes. These intermediate parallel pipes may include vortex purifiers or pressure strainers.

4 Claims, 7 Drawing Figures PATENTED FEB 1 1 I975 SHEET 30F 4 FIGA FIG.5

FIGS

VISCOSITY PERTURBATION DAMPER CONNECTED WITH DISTRIBUTION HEADER F PAPERMAKING MACHINE HEADBOX The present invention concerns means for damping the fast viscosity perturbations occurring in the pulp slurry flow conducted into the headbox of a paper making machine.

It is well-known thatthe amount of residual variation of the base weight of paper is held to be a criterion of the quality of operation of the headbox in a paper machine. And even then the cause responsible for the residual variation is thought to be associated with the flow rate quantities prevailing in the headbox (in the first place with the macro-turbulence). However, closer considerations of the cause of residual variation of base weight in paper, and measurements that have been carried out, have furnished reason to believe that the fast temporary viscosity variations occurring in the inlet pipe system also cause, in addition to base weight variation in the machine direction, the said random base weight variation and this in fact so that on the whole the explanatory contribution of viscosity quantities to the base weight variations would be greater in modern machines than that of velocity quantities.

It is well-known that the deaerator is sold owing to its process-stabilizing? effect. It appears as if the stabilizing effect of the deaerator were partly due to the fact that it equalizes fast viscosity perturbations. By the apparatus according to the present invention, equalization of these perturbations can be accomplished more efficiently and more expediently than in prior art. The apparatus is characterized in that in the pipe loop of the short circulation link leading to the headbox one or several viscosity perturbation dampers operating according to the multiple delay principle are incorporated.

The multiple delay principle is understood to mean a set-up wherein the pulp slurry is subdivided to pass along several paths of different lengths so that the result is distribution in time, or damping, of the viscosity perturbation. The principle and various embodiments of the invention are thought to be understandable in greater detail from the description following below and from the associated drawings, wherein FIG. 1 presents a typical application of the multiple delay principle, or a multiple delay line, FIG. la is a diagrammatic view, partly in section, of an apparatus of the present invention.

FIG. 2 shows the damping of a step perturbation in a multiple delay line,

FIG. 3 shows the damping of a sinusoidal perrturbation in a multiple delay line,

FIG. 4 shows a vortex purifier installation carried out in accordance with the multiple delay principle,

FIG. 5 shows a pressure strainer installation carried 'out in accordance with the multiple delay principle,

and

FIG. 6 shows a deaeration-vortex purifier carried out in accordance with the multiple delay principle.

The viscosity perturbance damper operating according to the multiple delay principle can be carried out most simply by means of the arrangement presented in FIG. 1. This comprises two parallel conduits, the inlet conduit 1 and the return conduit 2, which are connected by a number of intermediate pipes 3 disposed, for instance, with a uniform spacing. On passage from the inlet conduit 1 to the return conduit 2 the slurry flow is divided into parts, owing to the intermediate pipes 3, their flow path havin ,a greater length accordingly as the intermediate pip through which the partial flow passes is located farther away, in the direction of flow in the inlet conduit 1. Ifit is desired to maintain a constant velocity of flow in the conduits 1 and 2, they have to be made appropriately tapering towards their end over the section providedwith intermediate pipes. It is obvious that the damping characteristics of a viscosity perturbation damper, or mulltiple delay line, according to the figure are related to the number and spacing of the intermediate pipes 3' and to the size and shape of the inlet and return conduits.

FIG. la shows an apparatus having a pulp stock feed pump 6. A branch pipe 7 of the short circuit leads from the pump 6 toward the headbox 1B and is connected with the intake pipe 1 of the viscosity perturbation damper. The return conduit 2 of the viscosity perturbation damper is connected with the distribution header 14 of the headbox 8. A by-pass pipe 16 provided with a control valve 15 is also connected with the distribution header 14. The headbox 8 has perforated rolls 9, a flat wire 10 and a breast roll 17. There is also provided a wire basin 11 and a viscous: stock pipe 12 communicating with the return conduit 13. This return conduit 13 of the short circuit conducts water and the dilute pulp suspension from the wire basin 11 to the intake of the feed pump 6. It is apparent that the socalled short circuit is composed of the wire loops, the viscosity perturbation damper and the parts connected therewith.

FIG. 2 presents, as functions of time t, a step function-shaped pulse 0,- and the response 0,, into which a viscosity perturbation consistent with the pulse 0, is damped in a multiple delay line of the kind shown in FIG. 1. The number of intermediate pipes was assumed to be 10 and the time t, required for the flow to travel the distance between two such pipes was assumed to be 1 second. The dotted line represents the damping of a step perturbation of short duration.

The damping of a sinusoidal viscosity perturbation in a multiple delay line is dependent on the frequency of the perturbation. FIG. 3 displays roughly the ratio of response c and pulse 0,- as a function of the frequency fof the pulse in a case with n 20 and t, 0.5 sec. The graph reveals that no damping ensues if the frequency f equals /zt or a multiple hereof. This circumstance has to be taken into account when the multiple delay line is planned, if sinusoidal perturbations occur, by designing it so that for instance 1,. is not made constant throughout. It is also natural that perturbations having a low enough frequency are not damped.

In endeavours to damp the fast viscosity perturbations occurring in the pulp slurry flow conducted into the headbox of a paper machine by forming, in accordance with the present invention, in the branch pipe of the short circulation link leading to the headbox, viscosity perturbation dampers operating according to the multiple delay principle, it is most simple to employ a multiple delay line as shown in FIG. 1 and connected after all sources of perturbation possessing any. significance.

It is more advantageous, however, in accordance with FIGS. 4, 5 and 6 to connect the vortex purifiers 4 of a vortex purifying installation or deaeration-vortex purifying installation and/or the pressure strainers 5 of a pressure strainer installation in accordance with the multiple delay principle. The connections differ from the set-up in FIG. 1 in principle only in that the intermediate pipes 3 have been replaced with vortex purifiers 4 or pressure strainers 5. At the same time, the arrangement shown in FIG. 6 represents a case wherein in the inlet conduit 1,. may be constant, while in the return conduit t, is not constant.

It is then necessary in designing and dimensioning the installation to observe that the flow should enter the apparatus and return from it by the same end and that there are elements in one row only, so that the apparatus will be narrow and long and have a wide delay time distribution. Furthermore, the flow time from one element to another should be dimensioned to be long enough. When the short circulation link comprises several installations, such as a vortex purifying installation and a pressure strainer installation, all these are preferably connected in accordance with the multiple delay principle and they are so dimensioned with reference to each other that an optimum overall effect is obtained.

I claim:

1. In a paper machine having a headbox and a branch pipe of the short circulation link leading to the headbox, means for damping fast viscosity perturbances occurring in the pulp stock flow conducted into the headbox by the multiple delay principle, said means comprising a. a lengthy pulp stock input conduit located in connection with said branch pipe,

b. a lengthy pulp stock return conduit, running at least in its initial portion parallel with said input conduit and arranged to conduct the pulp stock into the headbox,

c. a plurality of parallel intermediate pipes spaced at a distance from each other, by which said input conduit and said return conduit are mutually connected, so that the directions of flow of the pulp stock are opposite in the parts of the input conduit and return conduit connected by said intermediate pipes, and so that the partial flows of the intermediate pipes are collected in the return conduit to form one single pulp stock flow before their conduction into the headbox.

2. Means according to claim 1, wherein said intermediate pipes consist of vortex purifiers of a vortexpurifying installation of the paper machine.

3. Means according to claim 1, wherein said intermediate pipes consist of pressure strainers of a pressure strainer installation.

4. Means according to claim 1, wherein said intermediate pipes consist of vortex purifiers of a deaerationvortex purifying installation. 

1. In a paper machine having a headbox and a branch pipe of the short circulation link leading to the headbox, means for damping fast viscosity perturbances occurring in the pulp stock flow conducted into the headbox by the multiple delay principle, said means comprising a. a lengthy pulp stock input conduit located in connection with said branch pipe, b. a lengthy pulp stock return conduit, running at least in its initial portion parallel with said input conduit and arranged to conduct the pulp stock into the headbox, c. a plurality of parallel intermediate pipes spaced at a distance from each other, by which said input conduit and said return conduit are mutually connected, so that the directions of flow of the pulp stock are opposite in the parts of the input conduit and return conduit connected by said intermediate pipes, and so that the partial flows of the intermediate pipes are collected in the return conduit to form one single pulp stock flow before their conduction into the headbox.
 2. Means according to claim 1, wherein said intermediate pipes consist of vortex purifiers of a vortex-purifying installation of the paper machine.
 3. Means according to claim 1, wherein said intermediate pipes consist of pressure strainers of a pressure strainer installation.
 4. Means according to claim 1, wherein said intermediate pipes consist of vortex purifiers of a deaeration-vortex purifying installation. 